Problem: Jessica did 75 more sit-ups than Umaima at night. Jessica did 78 sit-ups. How many sit-ups did Umaima do?
Explanation: Jessica did 78 sit-ups, and Umaima did 75 fewer than that, so find the difference. The difference is $78 - 75$ sit-ups. She did $78 - 75 = 3$ sit-ups.